Method for authenticating a mobile unit attached to a femtocell that operates according to code division multiple access

ABSTRACT

The present invention provides a method involving a femtocell in communication with an Internet Protocol Multimedia Subsystem (IMS) network. In one embodiment, the femtocell operates according to code division multiple access (CDMA) standards. The method includes receiving, from the femtocell and at a first secure entity in the IMS network, first authentication information generated by the mobile unit using a first random number broadcast by the femtocell in a global challenge. The method also includes receiving, from a second secure entity in the secure network, at least one security key formed based on the global challenge and second authentication information for uniquely challenging the mobile unit. In one embodiment, the second secure entity is a CDMA-based authentication server. The method further includes providing the security key(s) to the femtocell in response to authenticating the mobile unit based upon the second authentication information.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from prior United States provisionalpatent application Ser. No. 60/997,639, filed on Oct. 4, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to communication systems, and, moreparticularly, to wireless communication systems.

2. Description of the Related Art

Conventional wireless communication systems use a network of basestations to provide wireless connectivity to one or more mobile units.In some cases, the mobile units may initiate wireless communication withone or more base stations in the network, e.g., when the user of themobile unit would like to initiate a voice or data call. Alternatively,the network may initiate the wireless communication link with the mobileunit. For example, in conventional hierarchical wireless communications,a server transmits voice and/or data destined for a target mobile unitto a central element such as such as a Radio Network Controller (RNC).The RNC may then transmit paging messages to the target mobile unit viaone or more base stations. The target mobile unit may establish awireless link to one or more of the base stations in response toreceiving the page from the wireless communication system. A radioresource management function within the RNC receives the voice and/ordata and coordinates the radio and time resources used by the set ofbase stations to transmit the information to the target mobile unit. Theradio resource management function can perform fine grain control toallocate and release resources for broadcast transmission over a set ofbase stations.

Secure communications in a conventional hierarchical system, such as aCDMA system, are established based on secret information (e.g., anAuthentication Key) known only to the mobile unit and a secure entity inthe network. The HLR/AuC and the mobile unit may derive shared secretdata (SSD) from the Authentication Key (AK), e.g., using the CAVEalgorithm. The AK is a 64-bit primary secret key known only to themobile station and the HLR/AuC. This key is never shared with roamingpartners. The AK may be used to generate the SSD, which is a 128-bitsecondary key that can be calculated using the CAVE algorithm and can beshared with roaming partners. During authentication, the HLR/AuC and themobile unit both calculate an Authentication Response separately andindependently using shared inputs such as SSD, electronic serial number(ESN), Mobile Identity Number (MIN), and a shared Random Number (RAND).If the independently calculated results match up, then authentication isapproved and the mobile unit is allowed to register with the network.

The AK or SSD can be used to authenticate mobile units that areregistered in the network. For example, a base station may periodicallygenerate a random number (RAND) and broadcast the RAND. Mobile unitsthat receive the broadcast RAND compute an authentication algorithmoutput (AUTH) using the inputs including the RAND and the AK or SSD. TheAUTH and the associated RAND (or selected portions of the RAND) aresometimes referred to as a pair. The mobile unit may then transmit theAUTH/RAND pair to the base station, which may then pass this informationthrough the network on to the HLR/AuC. The HLR/AuC uses theauthentication algorithm, the stored value of the AK or SSD, other datacorresponding to each mobile unit, and the RAND to calculate theexpected value of AUTH. If this value matches the value transmitted bythe mobile unit, the mobile unit is authenticated. The base stationfrequently changes the value of RAND to ensure that the AUTH value isfresh and to reduce the possibility that previously generated AUTH/RANDresults may be captured by monitoring the air interface and replayed bya fraudulent mobile unit or mobile unit emulator. This technique isconsidered reasonably reliable, at least in part because base stationsare typically secure devices that are under the control of wirelesscommunication providers.

A unique challenge may also be used to challenge the mobile unit. In aunique challenge, an authentication center generates a unique randomnumber, which may be transmitted to the mobile unit. The mobile unituses a security algorithm to calculate a unique response to the uniquechallenge and then transmits information indicating the value of theunique response to the authentication center. The authentication centeralso executes the security algorithm to generate an expected value ofthe unique response. If the authentication center determines that theexpected value of the unique response is the same as the value providedby the mobile unit, then the mobile unit is authenticated. Otherwise, apossible security violation has occurred. Unique challenges aretypically used by systems that are not capable of authenticating onsystem access, e.g., using global challenges. Unique challenges can alsobe used as a backup authentication procedure if a valid exchange did notoccur upon system access.

One alternative to the conventional hierarchical network architecture isa distributed architecture including a network of access points, such asbase station routers, that implement distributed communication networkfunctionality. For example, each base station router may combine RNCand/or PDSN functions in a single entity that manages radio linksbetween one or more mobile units and an outside network, such as theInternet. Compared to hierarchical networks, distributed architectureshave the potential to reduce the cost and/or complexity of deploying thenetwork, as well as the cost and/or complexity of adding additionalwireless access points, e.g. base station routers, to expand thecoverage of an existing network. Distributed networks may also reduce(relative to hierarchical networks) the delays experienced by usersbecause packet queuing delays at the RNC and PDSN of hierarchicalnetworks may be reduced or removed.

At least in part because of the reduced cost and complexity of deployinga base station router, base station routers may be deployed in locationsthat are impractical for conventional base stations. For example, a basestation router may be deployed in a residence or building to providewireless connectivity to the occupants of the residents of the building.Base station routers deployed in a residence are typically referred toas home base station routers or femtocells because they are intended toprovide wireless connectivity to a much smaller area (e.g., a femtocell)that encompasses a residence. However, the functionality in a femtocellis typically quite similar to the functionality implemented in aconventional base station router that is intended to provide wirelessconnectivity to a macro-cell that may cover an area of approximately afew square kilometers. One important difference between a femtocell anda conventional base station router is that home base station routers aredesigned to be inexpensive plug-and-play devices that can be purchasedoff-the-shelf and easily installed by a lay person.

Femtocells do not typically include expensive security chips for storinginformation that can be used to establish secure communications betweenthe femtocell and mobile units. Furthermore, femtocells are intended tobe deployed in unsecured locations, such as a person's home or place ofbusiness. Consequently, femtocells are not considered trusted locationsfor storing secret keys or other information that may be used toauthenticate mobile units. A femtocell may therefore be modified tofraudulently represent a mobile unit if femtocells are configured togenerate the random numbers RAND used to authenticate mobile units. Forexample, an illegitimate femtocell may intercept a valid AUTH/RAND pairtransmitted between a legitimate mobile unit and a legitimate basestation. The illegitimate femtocell may then emulate the legitimatemobile unit using the intercepted AUTH/RAND pair. Since the femtocell isresponsible for generating RAND values, the network cannot determinewhether or not the AUTH/RAND pair transmitted by the illegitimatefemtocell corresponds to a fresh value of RAND.

SUMMARY OF THE INVENTION

The present invention is directed to addressing the effects of one ormore of the problems set forth above. The following presents asimplified summary of the invention in order to provide a basicunderstanding of some aspects of the invention. This summary is not anexhaustive overview of the invention. It is not intended to identify keyor critical elements of the invention or to delineate the scope of theinvention. Its sole purpose is to present some concepts in a simplifiedform as a prelude to the more detailed description that is discussedlater.

In one embodiment of the present invention, a method is providedinvolving a femtocell in communication with an Internet ProtocolMultimedia Subsystem (IMS) network. In one embodiment, the femtocelloperates according to code division multiple access (CDMA) standards.The method includes receiving, from the femtocell and at a first secureentity in the IMS network, first authentication information generated bythe mobile unit using a first random number broadcast by the femtocellin a global challenge. The method also includes receiving, from a secondsecure entity in the secure network, at least one security key formedbased on the global challenge and second authentication information foruniquely challenging the mobile unit. In one embodiment, the secondsecure entity is a CDMA-based authentication server. The method furtherincludes providing the security key(s) to the femtocell in response toauthenticating the mobile unit based upon the second authenticationinformation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numerals identify like elements, and in which:

FIG. 1 conceptually illustrates one exemplary embodiment of a wirelesscommunication system, in accordance with the present invention;

FIG. 2 conceptually illustrates one exemplary embodiment of a method ofauthenticating a mobile unit by providing a unique challenge when themobile unit registers, in accordance with the present invention;

FIG. 3 conceptually illustrates one exemplary embodiment of a method ofauthenticating a mobile unit based on a unique challenge during mobileunit registration, in accordance with the present invention;

FIG. 4 conceptually illustrates one exemplary embodiment of a method ofauthenticating a mobile unit by providing a unique challenge in responseto mobile unit origination, in accordance with the present invention;

FIG. 5 conceptually illustrates one exemplary embodiment of a method ofauthenticating a mobile unit based on a unique challenge during mobileunit origination, in accordance with the present invention; and

FIGS. 6A and 6B conceptually illustrate one alternative exemplaryembodiment of a method of authenticating a mobile unit based on a uniquechallenge, in accordance with the present invention.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the scope ofthe invention as defined by the appended claims.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions should be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

The present invention will now be described with reference to theattached figures. Various structures, systems and devices areschematically depicted in the drawings for purposes of explanation onlyand so as to not obscure the present invention with details that arewell known to those skilled in the art. Nevertheless, the attacheddrawings are included to describe and explain illustrative examples ofthe present invention. The words and phrases used herein should beunderstood and interpreted to have a meaning consistent with theunderstanding of those words and phrases by those skilled in therelevant art. No special definition of a term or phrase, i.e., adefinition that is different from the ordinary and customary meaning asunderstood by those skilled in the art, is intended to be implied byconsistent usage of the term or phrase herein. To the extent that a termor phrase is intended to have a special meaning, i.e., a meaning otherthan that understood by skilled artisans, such a special definition willbe expressly set forth in the specification in a definitional mannerthat directly and unequivocally provides the special definition for theterm or phrase.

FIG. 1 conceptually illustrates one exemplary embodiment of a wirelesscommunication system 100. In the illustrated embodiment, the wirelesscommunication system 100 includes one or more femtocells 105 forproviding wireless connectivity. The femtocells 105 may provide wirelessconnectivity according to standards and/or protocols including, but notlimited to, Code Division Multiple Access (CDMA) standards and/orprotocols, Universal Mobile Telecommunication Services (UMTS) standardsand/or protocols, Global System for Mobile communication (GSM) standardsand/or protocols, WiMAX standards and/or protocols, IEEE standardsand/or protocols, and the like. Furthermore, persons of ordinary skillin the art having benefit of the present disclosure should appreciatethat the present invention is not limited to using femtocells 105 toprovide wireless connectivity. In alternative embodiments, devices suchas base stations, base station routers, access points, access networks,and the like may be used to provide wireless connectivity in thewireless communication system 100.

The femtocell 105 is intended to provide wireless coverage to an areathat approximately encompasses a building that includes one or moremobile units 110 that are granted access to the femtocell 105. Themobile units 110 may be registered with the femtocell 105 using avariety of techniques including having a user enter an InternationalMobile Subscriber Identity (IMSI) for the registered mobile units 110via a webpage, using a handshaking protocol between the mobile units 110and the femtocell 105, and the like. A list of the registered mobileunits 110 is then made available to the femtocell 105. In oneembodiment, the femtocell 105 contains a database including the IMSIvalues for the registered mobile units 110. In the illustratedembodiment, the mobile unit 110 is a code division multiple access(CDMA)-based wireless mobile unit 110. However, persons of ordinaryskill in the art having benefit of the present disclosure shouldappreciate that the present invention is not limited to CDMA-basedmobile units 110.

The femtocell 105 provides access to the wireless communication system100 via an Internet Protocol Multimedia Subsystem (IMS) network 115(indicated by the dashed box). In various alternative embodiments thefemtocell 105 may be coupled to the IMS network 115 by a variety offunctional elements. For example, in FIG. 1 the femtocell 105 is coupledto a digital subscriber line (DSL) or cable modem network 120, which iscoupled to a femto network gateway 125. An Operations Administration andMaintenance (OA & M) server 130 may be coupled to the femto networkgateway 125 and may be used to establish communications between thefemtocell 105 and an Internet Protocol (IP) network 135 via the femtonetwork gateway (FNG) 125. For example, an IPSec tunnel may be formedbetween the femtocell 105 and the femto network gateway 125. However,persons of ordinary skill in the art having benefit of the presentdisclosure should appreciate that this exemplary embodiment is notintended to limit the present invention to this particular networkarchitecture.

The IMS network 115 is a Session Initiation Protocol (SIP) based networkthat supports communication over the internet by many types of handsets.For example, these handsets (such as the mobile unit 110 combined withthe femtocell 105) may use Voice over Internet Protocol (VoIP) and othermethods to transfer data and voice in real time applications across theIP network 135. The IMS network 115 includes a Home Subscriber Server(HSS) 140, which is a master user database that supports the IMS networkentities that handle calls. The HSS 140 may contain subscription-relatedinformation (user profiles), perform authentication and authenticationof the user, and can provide information about the user's physicallocation. The IMS network 115 may also include one or more Call SessionControl Function (CSCF) entities 145 that are used to process SIPsignaling packets in the IMS network 115. Although the CSCF entities 145are shown as a single functional block in FIG. 1, persons of ordinaryskill in the art having benefit of the present disclosure shouldappreciate that the CSCF entities 145 may include multiple entities suchas a serving CSCF, a proxy CSCF, an interrogating CSCF, and the like,which may be implemented in one or more other functional and/or physicalentities. A Mobility Management Application Server (MMAS) 150 is used tocoordinate and manage functions related to the mobility of the mobileunits 110.

The femtocell 105 may transmit global challenges to the mobile unit 110an overhead channel. In one embodiment, the global challenge is based ona global random number that is generated at the femtocell 105. On everysystem access, mobile units are required to compute a response usingsecret data (SSD or AK) and to return the response and at least aportion of the random number to the system for verification. Thefemtocell 105 uses the global random number and the response toauthenticate the mobile unit 110 and to establish a secure communicationlink over the air interface with the mobile unit 110. However, thefemtocell 105 may not be a trusted element of the wireless communicationsystem 100. For example, the femtocell 105 may not be physically securebecause it may be located in a user's residence or place of business.Consequently, the service provider may not be able to ensure that thefemtocell 105 cannot be accessed by an unauthorized user who may attemptto modify or hack the femtocell 105. Furthermore, the femtocell 105 maybe susceptible to hacking over a network. For example, the user of thefemtocell 105 may not provide sufficient firewall protection, virusprotection, and the like, which may permit unauthorized users to hackinto the femtocell 105. Since the femtocell 105 is not a trusted elementof the system 100, global challenges issued by the femtocell 105 (aswell as authentications based on these global challenges) may also besuspect.

In contrast, the entities in the IMS network 115 are trusted or secureentities. For example, the MMAS 150 may be physically secure because itis located in a building that is under the control of the serviceprovider. Consequently, the service provider may be able to ensure thatthe MMAS 150 cannot be accessed by an unauthorized user who may attemptto modify or hack the femtocell 105. Furthermore, the MMAS 150 may beprotected from hacking using firewall protection, virus protection, andthe like, which may prevent unauthorized access to the MMAS 150. Otherentities in the network, such as a home location register/authenticationcenter (HLR/AuC) 160 that is used to generate and provide one or morekeys to the femtocell 105 and/or the mobile unit 110, may also beconsidered relatively trusted and/or secure because they are under thecontrol of a service provider.

Trusted and/or secure entities within (or securely coupled to) the IMSnetwork 115 may therefore be used to authenticate the mobile unit 110using a unique challenge that can be issued following a suspect globalchallenge. In one embodiment, the mobile unit 110 may respond to a(potentially suspect) global challenge issued by the femtocell 105 byforwarding a global authentication response to the IMS network 115,which may verify the global authentication response and generatesecurity information such as a session keys in cooperation with theHLR/AuC 160. The IMS network 115 may then create and send a uniquechallenge to the mobile unit 110 via the femtocell 105. Upon receivingthe unique challenge, the mobile unit 110 generates a uniqueauthentication response that is forwarded to the IMS network 115 forverification. Once the mobile unit 110 has been authenticated by thetrusted and/or secure entity, the IMS network 115 may provide callprocessing services or security information, such as one or more keysgenerated at the home location register/authentication center (HLR/AuC)160, to the femtocell 105.

FIG. 2 conceptually illustrates one exemplary embodiment of a method 200of authenticating a mobile unit (UE) by providing a unique challengewhen the mobile unit registers with the network. In the illustratedembodiment, a femtocell or base station router (BSR) is used to providewireless connectivity to the mobile unit. The femtocell iscommunicatively coupled to an IMS network that includes a serving CSCF(S-CSCF), a proxy CSCF (P-CSCF), an interrogating CSCF (I-CSCF), a homesubscriber server (HSS), and a mobility management application server(MMAS). The IMS network is also in communication with a home locationregister/authentication center (HLR/AuC). Persons of ordinary skill inthe art having benefit of the present disclosure should appreciate thatthe elements shown in FIG. 2 are illustrative and are not intended tolimit the present invention. In alternative embodiments, more or fewerelements that perform more or fewer functions may be included.

In the illustrated embodiment, the femtocell creates a global randomnumber (RAND) and broadcasts this random number (RAND) in the overheadmessage train, as indicated by the arrow 205. The mobile unit calculatesa global authentication response (AUTHR) using the global random numberand a key such as an SSD key that is known only to the mobile unit andthe HLR/AuC. The mobile unit may then send a registration message to thefemtocell, as indicated by the arrow 210. The registration message sentby the mobile unit may be a SIP registration message that includes theglobal random number, the global authentication response, a mobile unitidentifier, and an electronic subscriber number. The femtocell forwardsthe registration message to the P-CSCF, which may then forward theregistration message to the I-CSCF, as indicated by the arrows, 215,220. The I-CSCF may send an interrogation message to the home subscriberserver to determine the appropriate S-CSCF for the mobile unit, asindicated by the arrow 225. The home subscriber server replies withinformation indicating the selected S-CSCF, as indicated by the arrow230. The registration message is then forwarded to the selected S-CSCF,as indicated by the arrow 240.

The S-CSCF sends a message to the home subscriber server to ask whetherIMS authentication needs to be performed for the mobile unit, asindicated by the arrow 245. For example, the S-CSCF may send (at 245) amobile authentication request (MAR) to the home subscriber server. Thehome subscriber server then returns information indicating whether ornot IMS authentication needs to be performed for the mobile unit, asindicated by the arrow 250. If the message from the home subscriberserver indicates that it is not necessary to authenticate the mobileunit, then IMS authentication may be skipped (at 255). If the messagefrom the home subscriber server indicates that it is necessary toauthenticate the mobile unit, then IMS authentication may be performedwith a User Agent at the femtocell (at 255). In either case, the S-CSCFtransmits a request for a mobile unit service profile to the homesubscriber server, as indicated by the arrow 260, and the homesubscriber server returns the service profile for the mobile unit to theS-CSCF, as indicated by the arrow 265. If the IMS authentication stepwas skipped, then the S-CSCF tells the femtocell that registration iscomplete (e.g., by transmitting a 200-OK message) and the femtocell mayrespond with an acknowledgment message, as indicated by the doublearrows 270.

In one embodiment, the femtocell may subscribe (at 275) to its IMSregistration status, e.g., by transmitting an SUBSCRIBE message to theS-CSCF, which may return a message (such as a 200-OK message) confirmingthe subscription. If the CDMA authentication of the mobile unit failslater in the challenge/response sequence, then the mobility managementapplication server can inform the S-CSCF that the IMS registration hasfailed, e.g., by providing a 4xx failure message instead of a 200-OKmessage. Since the mobility management application server receives theregistration message as a third party registration message based on aninitial filter criteria in the user profile stored at the S-CSCF, theregistration failure message may cause the S-CSCF to de-register themobile unit. De-registration of the mobile unit may mean that thepreviously completed IMS registration would be torn down. A user agentat the femtocell should receive a notification when the registration istorn down since the femtocell subscribed to changes in its IMSregistration status. Thus, the user agent at the femtocell is in aposition to clean up whatever needs to be cleaned up. In one embodiment,the user agent may commit suicide.

The S-CSCF may send a registration message to the mobility managementapplication server, as indicated by the arrow 280. In one embodiment,the S-CSCF sends (at 280) a SIP third party registration message thatincludes information indicating the mobile unit identifier, theelectronic serial number, the authentication response, and the globalrandom number. In response to receiving the registration message, themobility management application server authenticates (at 285) the mobileunit using a unique challenge/response pair provided by the HLR/AuC.Results of the authentication procedure are then transmitted to theS-CSCF a message, such as a 200-OK registration message, as indicated bythe arrow 290.

FIG. 3 conceptually illustrates one exemplary embodiment of a method 300of authenticating a mobile unit based on a unique challenge duringmobile unit registration. Some or all of the method 300 may beimplemented as part of the step 285 depicted in FIG. 2. In theillustrated embodiment, the S-CSCF sends a registration message such asa SIP third party registration message to the mobility managementapplication server, as indicated by the arrow 305. In response toreceiving the registration message, the mobility management applicationserver requests a unique challenge/response pair that may be used toauthenticate the mobile unit. For example, the mobility managementapplication server may function like a visitor location register (VLR)and send an authentication request for the unique challenge/responsepair to the HLR/AuC, as indicated by the arrow 310. The HLR/AuC may thenreturn the requested unique challenge/response pair, such as a uniquerandom number (RANDU) and a unique authentication response (AUTHU).

The mobility management application server can challenge the mobile unitusing the provided unique challenge/response pair. In the illustratedembodiment, the mobility management application server forwards amessage, such as a SIP message to the S-CSCF, which forwards the messageto the femtocell, as indicated by the arrows 320, 325. The messageincludes the unique challenge represented by the unique random numbergenerated by the HLR/AuC for the mobile unit. The femtocell then forms aunique challenge message using the received unique challenge randomnumber and transmits it to the mobile unit, as indicated by the arrow330. Upon receipt of the unique challenge, the mobile unit generates aunique authentication response (AUTHU) using the provided unique randomnumber and a security key known to the mobile unit. The mobile unitreturns a challenge response message including the unique random numberand the computed authentication response (RANDU/AUTHU) to the femtocell,as indicated by the arrow 335. The femtocell may then transmit thecomputed authentication response (AUTHU) to the S-CSCF, which may forthis response to the mobility management application server, asindicated by the arrows 340, 345. For example, the computedauthentication response may be transmitted in a 200-OK response message.

The mobility management application server may authenticate (at 350) themobile unit using the authentication response values provided by themobile unit and the HLR/AuC. In one embodiment, the mobility managementapplication server compares (at 350) the authentication response valuesprovided by the mobile unit and the HLR/AuC and authenticate (at 350)the mobile unit if these two values match. If the mobile unit issuccessfully authenticated (at 350), then the mobility managementapplication server transmits a registration notification to the HLR/AuC,as indicated by the arrow 355. The HLR/AuC may transmit a confirmationin response to receiving the registration notification, as indicated bythe arrow 360. In one embodiment, the confirmation 360 may include avisitor location register profile associated with the mobile unit.

If the mobile unit has been successfully authenticated (at 350) andregistered (at 355, 360), then the mobility management applicationserver may transmit a registration acknowledgment message to the S-CSCF,as indicated by the arrow 365. For example, the mobility managementapplication server may transmit (at 365) a 200-OK message that indicatesthat the registration and authentication of the mobile unit has beensuccessful. In one embodiment, the S-CSCF may proceed to perform suchtasks as using its list of rules to determine whether or not any otherapplication servers are supposed to be notified in the event that themobile unit is successfully registered. However, persons of ordinaryskill in the art having benefit of the present disclosure shouldappreciate that determining whether to notify other application serversis only one example of an intelligent network “trigger” and the list ofrules on the S-CSCF are examples of instructions that may be used todetermine when to fire these triggers. In one embodiment, the triggersprovide application servers with the opportunity to process one or moreSIP messages.

FIG. 4 conceptually illustrates one exemplary embodiment of a method 400of authenticating a mobile unit (UE) by providing a unique challenge inresponse to mobile unit origination. In the illustrated embodiment, afemtocell or base station router (BSR) is used to provide wirelessconnectivity to the mobile unit. The femtocell is communicativelycoupled to an IMS network that includes a serving CSCF (S-CSCF), a proxyCSCF (P-CSCF), an interrogating CSCF (I-CSCF), and a mobility managementapplication server (MMAS). The IMS network is also in communication witha home location register/authentication center (HLR/AuC) and another enduser (END), such as another mobile unit or other communication device.Persons of ordinary skill in the art having benefit of the presentdisclosure should appreciate that the elements shown in FIG. 4 areillustrative and are not intended to limit the present invention. Inalternative embodiments, more or fewer elements that perform more orfewer functions may be included.

In the illustrated embodiment, the femtocell creates a global randomnumber (RAND) and broadcasts this random number (RAND) in the overheadmessage train, as indicated by the arrow 405. The mobile unit calculatesa global authentication response (AUTHR) using the global random numberand a key such as an SSD key that is known only to the mobile unit andthe authentication center (AuC). If the mobile unit wants to originateservice, the mobile unit may send an origination message to thefemtocell, as indicated by the arrow 410. For example, the mobile unitmay transmit (at 410) a CDMA origination message including the globalrandom number, the authentication response, a mobile unit identifier,and an electronic subscriber number. The mobile unit may also transmitthe dialed digits of the other end-user. The femtocell forms aninvitation message and forwards the invitation message to the P-CSCF,which may then forward the invitation message to the I-CSCF, asindicated by the arrows, 415, 420. In one embodiment, the invitationmessage is a SIP INVITE message that includes the global random number,the authentication response, a mobile unit identifier, and an electronicsubscriber number. The S-CSCF may then forward the invitation message tothe mobility management application server, as indicated by the arrow430.

Upon receipt of the invitation message, the mobility managementapplication server attempts (at 435) to authenticate the mobile unit andmay also create one or more security keys, such as an SMEKEY and/or aPLCM key that may be used for encrypting messages or voice traffic. Inone embodiment, the steps that are used to authenticate the mobile unitand create the CDMA encryption keys may be performed concurrently and/orsynchronously. However, persons of ordinary skill in the art havingbenefit of the present disclosure should appreciate that the steps mayalternatively be distributed within the flow of call setup messages toattempt to optimize the procedure. For example, a unique challenge couldbe derived prior to the call and stored by the mobility managementapplication server for immediate use at the call time. If the mobileunit is successfully authenticated (at 435) and the mobility managementapplication server may transmit an invitation message to the end user(END), as indicated by the arrow 440. For example, the mobilitymanagement application server may transmit (at 440) an INVITE message tothe end-user. A response message, such as a 180-Ringing message, maythen be returned to the mobility management application server, whichmay forward this message to the mobile unit via the femtocell, asindicated by the arrows 445, 450. An audible ringing message may also beprovided to the mobile unit, as indicated by the arrow 455. A messageindicating that the user has answered the call, such as a 200-OK-Answermessage, may be transmitted to the femtocell via the mobility managementapplication server if the end-user accepts the call, as indicated by thearrows 460, 465.

FIG. 5 conceptually illustrates one exemplary embodiment of a method 500of authenticating a mobile unit based on a unique challenge duringmobile unit origination. Some or all of the method 500 may beimplemented as part of the step 435 depicted in FIG. 4. In response toreceiving an origination requests, such as a SIP INVITE message, themobility management application server sends an authentication requestto the HLR/AuC, as indicated by the arrow 505. In one embodiment, theauthentication request includes the global random number, the globalauthentication response computed by the mobile unit, some or all of thedialed digits corresponding to the other end user, a mobile unitidentifier, the electronic serial number, and any other information. TheHLR/AuC may then provide security information such as the SMEKEY and/orPLCM key associated with the originated call, as indicated by the arrow510. The mobility management application server may also transmit anauthentication request to the HLR/AuC, as indicated by the arrow 515.The authentication request includes a request for a uniquechallenge/response pair associated with the originating mobile unit. TheHLR/AuC may then return (at 520) the requested challenge/response pair,which may be a unique random number (RANDU) and a corresponding uniqueauthentication response (AUTHU).

The mobility management application server may then forward a uniquechallenge including the unique random number to the S-CSCF, which mayforward the unique challenge to the femtocell, as indicated by thearrows 525, 530. The femtocell may use the provided unique random numberto issue a unique challenge to the mobile unit, as indicated by thearrow 535. In response to the unique challenge, the mobile unit maycompute an authentication response using the provided unique randomnumber and a security key stored on the mobile unit. The uniqueauthentication response may then be transmitted back to the femtocell,as indicated by the arrow 540. The femtocell may then transmit thecomputed authentication response (AUTHU) to the S-CSCF, which mayforward this response to the mobility management application server, asindicated by the arrows 545, 550. For example, the computedauthentication response and the unique random number may be transmittedin a 200-OK response message.

The mobility management application server may authenticate (at 555) themobile unit using the unique authentication response values provided bythe mobile unit and the authentication center. In one embodiment, themobility management application server compares (at 555) theauthentication response values provided by the mobile unit and theauthentication center and authenticate (at 555) the mobile unit if thesetwo values match. If the mobile unit is successfully authenticated (at555), then the mobility management application server may transmitsecurity information for the call to the femtocell via the S-CSCF, asindicated by the arrows 560, 565. For example, the mobility managementapplication server may transmit (at 560, 565) a 200-OK message thatindicates that the registration and authentication of the mobile unithas been successful and includes the previously determined SMEKEY and/orPLCM key. At this point the femtocell has the encryption keys that maybe used to encrypt the traffic channel for the call. The femtocell mayconfirm receipt of the security information by transmitting a messageback to the mobility management application server, as indicated by thearrows 570, 575. For example, the femtocell may transmit (at 570, 575) a200-OK message to the mobility management application server.

FIGS. 6A and 6B conceptually illustrate one alternative exemplaryembodiment of a method 600 of authenticating a mobile unit based on aunique challenge. In the illustrated embodiment, a femtocell or basestation router (BSR) is used to provide wireless connectivity to themobile user equipment (UE). The femtocell is communicatively coupled toan IMS network that includes a serving CSCF (S-CSCF), a proxy CSCF(P-CSCF), an interrogating CSCF (I-CSCF), and a mobility managementapplication server (MMAS). The IMS network is also in communication witha home location register/authentication center (HLR/AuC) and another enduser (END), such as another mobile unit or other communication device.Persons of ordinary skill in the art having benefit of the presentdisclosure should appreciate that the elements shown in FIGS. 6A and 6Bare illustrative and are not intended to limit the present invention. Inalternative embodiments, more or fewer elements that perform more orfewer functions may be included.

The mobility management application server sends an authenticationrequest to the authentication center, as indicated by the arrow 601. Inone embodiment, the authentication request may include, a mobile unitidentifier, the electronic serial number, and any other information. TheHLR/AuC may then respond with a message that includes information thatcan be used to later form a unique challenge to the mobile unit. In theillustrated embodiment, the request (at 601) and response (at 602) areperformed prior to the mobile unit requesting access to the system,e.g., during a registration request or an origination request. Forexample, the request (at 601) and response (at 602) may be performedduring a previous system access by the mobile unit and the uniqueauthentication information (e.g., the RANDU/AUTHU pair) may be stored atthe MMAS until the mobile unit requests access to the system.

In the illustrated embodiment, the femtocell periodically creates aglobal random number (RAND) and broadcasts this random number (RAND) inthe overhead message train, as indicated by the arrow 603. The mobileunit may then calculate an authentication response (AUTHR) using theglobal random number and a key such as an SSD key that is known only tothe mobile unit and the authentication center (AuC). If the mobile unitwants to originate service, the mobile unit may send an originationmessage to the femtocell, as indicated by the arrow 604. For example,the mobile unit may transmit (at 604) a CDMA origination messageincluding the global random number, the authentication response, amobile unit identifier, and an electronic subscriber number. The mobileunit may also transmit the dialed digits of the other end-user. Thefemtocell forms an invitation message and forwards the invitationmessage to the P-CSCF, which may then forward the invitation message tothe S-CSCF, as indicated by the arrows, 605, 606. In one embodiment, theinvitation message is a SIP INVITE message that includes the globalrandom number, the authentication response, a mobile unit identifier,and an electronic subscriber number. The S-CSCF may then forward theinvitation message to the mobility management application server, asindicated by the arrow 607.

The mobility management application server may then forward a challengeincluding the unique random number to the S-CSCF, which may forward thechallenge to the femtocell, as indicated by the arrows 608, 609. Sincethe unique authentication information has already been calculated andstored, the MMAS can transmit (at 608) the unique challenge directly inresponse to receiving the invitation message, instead of having to firstrequest the unique challenge information from the AuC. The femtocell mayuse the provided unique random number (RANDU) to issue a uniquechallenge to the mobile unit, as indicated by the arrow 610. Themobility management application server may also send an authenticationrequest to the authentication center, as indicated by the arrow 611. Inone embodiment, the authentication request may include the global randomnumber, the global authentication response computed by the mobile unit,a mobile unit identifier, the electronic serial number, and any otherinformation. The authentication center may then provide securityinformation such as the SMEKEY and/or PLCM key associated with theoriginated call, as indicated by the arrow 612. The request for thesecurity information (at 611) and the response including the securityinformation (at 612) may be performed concurrently with some or all ofthe steps 608, 609, 610.

In response to the unique challenge (at 610), the mobile unit maycompute an authentication response using the provided unique randomnumber and a secret key stored on the mobile unit. The uniqueauthentication response may then be transmitted back to the femtocell,as indicated by the arrow 613. The femtocell may then transmit thecomputed authentication response (AUTHU) to the S-CSCF, which mayforward this response to the mobility management application server, asindicated by the arrows 614, 615. For example, the computedauthentication response and the unique random number may be transmittedin a 200-OK response message.

The mobility management application server may authenticate (at 616) themobile unit using the authentication response (AUTHU) values provided bythe mobile unit and the authentication center. In one embodiment, themobility management application server compares (at 616) theauthentication response values provided by the mobile unit and theauthentication center and authenticate (at 616) the mobile unit if thesetwo values match. If the mobile unit is successfully authenticated (at616), then the mobility management application server may transmitsecurity information for the call to the femtocell via the S-CSCF, asindicated by the arrows 617, 618. For example, the mobility managementapplication server may transmit (at 617, 618) a 200-OK message thatindicates that the registration and authentication of the mobile unithas been successful and includes the previously determined SMEKEY and/orPLCM key. At this point the femtocell has the encryption keys that maybe used to encrypt the traffic channel for the call. The femtocell mayconfirm receipt of the security information by transmitting a messageback to the mobility management application server, as indicated by thearrows 619, 620. For example, the femtocell may transmit (at 619, 620) a200-OK message to the mobility management application server.

In some cases, it is possible that an SSD update may have occurredbetween creation of the authentication information (at 601, 602) andauthentication (at 616) of the mobile unit. If this occurs and a freshset of AUTHU/RANDU data is not retrieved from the HLR/AuC, the mobileunit will not be authenticated, even if it returns the right AUTHU.However, the SSD updates happen through the femtocell serving system,which is the MMAS in this case. Thus, the MMAS would be involved andknow it must get a fresh RANDU/AUTHU pair. When the update happensthrough the macrocell (e.g., because the handset has moved from thefemto cell to the macro cell), the update should cause a registration atthe HLR/AuC and a notice of deregistration should be sent to the formerVLR, which is the MMAS. The MMAS would therefore know that its currentpair is not fresh so that when the handset registers back with the femtocell, the MMAS can get a fresh RANDU/AUTHU which would be used duringcall next system access.

Once the mobile unit has been successfully authenticated (at 616) themobility management application server may transmit an invitationmessage to the end user (END), as indicated by the arrow 621. Forexample, the mobility management application server may transmit (at621) an INVITE message to the end-user. A response message, such as a180-Ringing message, may then be returned to the mobility managementapplication server, which may forward this message to the mobile unitvia the femtocell, as indicated by the arrows 622, 623. An audibleringing message may then be transmitted to the mobile unit, as indicatedby the arrow 624. A message indicating that the user has answered thecall, such as a 200-OK-Answer message, may be transmitted to thefemtocell via the mobility management application server if the end-useraccepts the call, as indicated by the arrows 625, 626.

Portions of the present invention and corresponding detailed descriptionare presented in terms of software, or algorithms and symbolicrepresentations of operations on data bits within a computer memory.These descriptions and representations are the ones by which those ofordinary skill in the art effectively convey the substance of their workto others of ordinary skill in the art. An algorithm, as the term isused here, and as it is used generally, is conceived to be aself-consistent sequence of steps leading to a desired result. The stepsare those requiring physical manipulations of physical quantities.Usually, though not necessarily, these quantities take the form ofoptical, electrical, or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise, or as is apparent from the discussion,terms such as “processing” or “computing” or “calculating” or“determining” or “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data represented as physical, electronicquantities within the computer system's registers and memories intoother data similarly represented as physical quantities within thecomputer system memories or registers or other such information storage,transmission or display devices.

Note also that the software implemented aspects of the invention aretypically encoded on some form of program storage medium or implementedover some type of transmission medium. The program storage medium may bemagnetic (e.g., a floppy disk or a hard drive) or optical (e.g., acompact disk read only memory, or “CD ROM”), and may be read only orrandom access. Similarly, the transmission medium may be twisted wirepairs, coaxial cable, optical fiber, or some other suitable transmissionmedium known to the art. The invention is not limited by these aspectsof any given implementation.

The particular embodiments disclosed above are illustrative only, as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Furthermore, no limitations are intended to thedetails of construction or design herein shown, other than as describedin the claims below. It is therefore evident that the particularembodiments disclosed above may be altered or modified and all suchvariations are considered within the scope of the invention.Accordingly, the protection sought herein is as set forth in the claimsbelow.

What is claimed is:
 1. A method involving a femtocell in communicationwith a secure network, comprising: authenticating, at a first secureentity in the secure network, a mobile unit using a globalauthentication response received from the mobile unit, wherein theglobal authentication response is generated by the mobile unit using afirst security key and a first random number , wherein the firstsecurity key is unknown to the femtocell; receiving, at the first secureentity and from a second secure entity in the secure network, at leastone second security key formed based on the global challenge;transmitting a unique challenge comprising a second random number fromthe first secure entity to the mobile unit via the femtocell; receiving,at the first secure entity and from the femtocell, a unique challengeresponse generated by the mobile unit using the second random number andthe first security key; and providing said at least one second securitykey to the femtocell in response to the first secure entityauthenticating the mobile unit based on the second random number.
 2. Themethod of claim 1, wherein authenticating the mobile unit using theglobal authentication response comprises authenticating the mobile unitusing a global authentication response comprising information indicatingan identifier uniquely identifying the first mobile unit, the firstrandom number, and an authentication response computed by the mobileunit based on the first random number and the first security key knownby the mobile unit and not known by the femtocell.
 3. The method ofclaim 2, wherein transmitting the unique challenge comprisestransmitting a unique challenge formed by the femtocell using the secondrandom number and an autheritication response that is unique to themobile unit, the second secure entity determining the authenticationresponse based on the identifier uniquely identifying the first mobileunit.
 4. The method of claim 3, comprising providing the second randomnumber to the femtocell so that the femtocell can transmit the uniquechallenge including the second random number to the mobile unit.
 5. Themethod of claim 4, comprising receiving, at the first secure entity andin response to providing the second random number, informationindicating the second random number and an authentication responsecomputed by the mobile unit based on the second random number.
 6. Themethod of claim 5, comprising authenticating the mobile unit if theauthentication response computed by the mobile unit based on the secondrandom number corresponds to the authentication response received fromthe second secure entity.
 7. The method of claim 1, wherein requestingat least one second security key from the second secure entity comprisesrequesting session keys for encryption of signaling and bearer traffic.8. The method of claim 1, wherein authenticating the mobile unitcomprises authenticating the mobile unit in response to at least one ofa registration message transmitted from the mobile unit to the femtocellor an origination message transmitted from the mobile unit to thefemtocell.
 9. A method involving a femtocell that operates according tocode division multiple access (CDMA) standards, the femtocell is alsoconfigured to communicate with an Internet Protocol Multimedia Subsystem(IMS) network, comprising: authenticating, at a first secure entity inthe IMS network, a mobile unit using a global authentication responsereceived from the mobile unit, wherein the global authenticationresponse is generated by the mobile unit using a first random number anda first security key that is unknown to the femtocell; receiving, at thefirst secure entity and from a CDMA-based authentication serverconnected to the IMS network, at least one encryption key formed basedon the global challenge; transmitting a unique challenge comprising asecond random number from the first secure entity to the mobile unit viathe femtocell; receiving, at the first secure entity and from thefemtocell, a unique challenge response generated by the mobile unitusing the second random number and the first security key; and providingsaid at least one encryption key to the femtocell in response to thefirst secure entity authenticating the mobile unit based on the secondrandom number.
 10. The method of claim 9, wherein authenticating themobile unit comprises authenticating the mobile unit using a globalauthentication response comprising indicating an electronic serialnumber uniquely identifying the first mobile unit, the first randomnumber, and an authentication response computed by the mobile unit basedon the first random number and the first security key known by themobile unit and not known by the femtocell.
 11. The method of claim 10,comprising forming the unique challenge using information indicating thesecond random number and an authentication response that is unique tothe mobile unit, the CDMA-based authentication server determining theauthentication response based on the electronic serial number uniquelyidentifying the first mobile unit.
 12. The method of claim 11, whereintransmitting the unique challenge comprises providing the second randomnumber to the femtocell so that the femtocell can transmit the uniquechallenge including the second random number to the mobile unit.
 13. Themethod of claim 12, wherein authenticating the mobile unit comprisesreceiving, at the first secure entity and in response to providing thesecond random number, information indicating the second random numberand an authentication response computed by the mobile unit based on thesecond random number.
 14. The method of claim 13, wherein authenticatingthe mobile unit comprises authenticating the mobile unit if theauthentication response computed by the mobile unit based on the secondrandom number corresponds to the authentication response received fromthe CDMA-based authentication server.
 15. The method of claim 9, whereinrequesting at least one encryption key from the CDMA-basedauthentication server comprises requesting at least one of a SMEKEY or aPublic Long Code Mask key.
 16. The method of claim 9, whereinauthenticating the mobile unit comprises authenticating the mobile unitusing the global authentication response received in response to atleast one of a registration message transmitted from the mobile unit tothe femtocell or an origination message transmitted from the mobile unitto the femtocell.